I am doing a hygrolon background on the glass, I spread a thin layer of silicone and intend to put on a layer of gorilla glue then stick the Hygrolon to that. My question is how long should I let the silicone cure before i add the gorilla glue. I mean does it need to be fully cured, just feel dry to the touch, or will it cure on out even after the gorilla glue layer has been added?

Theres no reason to use the gorilla glue - you can apply the hygrolon directly to the silicone before it cures. Hyrgolon to silicone will likely hold better than hygrolon to gorilla glue to silicone anyway.